The development of fibers which are capable of transmitting light over long distances with relatively low losses began in the mid-to-late 1960's. What has evolved are fiber optics constructions which consist of at least two and generally three components, namely a core, a cladding, and, optionally, a protective coating for the cladded core. The core, which actually performs the light transmitting function, is generally either siliceous glass or an amorphous organic polymer and is physically located at the center of the construction. In order to avoid excessive losses of light in a transverse direction, the core must be coated of "clad" with a material that possesses a refractive index lower than that of the core. This cladding material can be an organic polymer, and because of their relatively low refractive indices, fluorinated polymers and polysiloxanes have emerged as important cladding materials. In addition to proper light handling characteristics, other desirable features of polymeric claddings are thermal and chemical stablity to include resistance to moisture; low surface tack; toughness and abrasion resistance; and, especially important, a high level of adherence to the core material. Additional information concerning fiber optical constructions may be obtained from a book entitled "Optical Fiber Telecommunication", edited by S. E. Miller and A. G. Chynoweth, Academic Press: New York, 1979; Chapter 10 by L. L. Blyler, Jr., et al., deals specifically with claddings and is incorporated as a general reference.
As a general rule, silanol groups reduce the light transmitting qualities of a siliceous core and it is desirable to minimize their concentration. What is apparent from references such as A. Sartre, et al., J. Non-Cryst. Solids, 66, 467 (1987), however, is that despite efforts to eliminate silanol groups from siliceous cores, silanol groups persist in low concentration, especially on the core surface. Therefore, as a siliceous molten core emerges from the furnace of a typical draw tower arrangement for preparing optical fibers, the external surface of the core contains silanol groups or will soon develop them.
Attempts to covalently bond to a siliceous substrate (especially glass) have largely involved reactions of alkoxysilanes with surface silanol groups as depicted in equation (1), and a recent paper by J. P. Blitz, et al., J. Am. Chem. Soc., 109 7141 (1987) is cited as a general reference examining the various possible linkages and experimental techniques utilized to probe the nature of the surface reaction. ##STR1##
While the product of equation (1) is relatively stable and chemically inert, there is a problem in that at least one molecule of an alcohol (ROH), which somehow must be removed from the system, is produced for every linkage formed. Removal of the alcohol can be a significant problem when relatively hydrophobic polymers are involved. These polymers do not allow facile passage and removal of the alcohol molecule. The presence of residual alcohol can lead to voids and imperfections in a resultant coating and can oftentimes be a problem with an alkoxysilane/fluoropolymer cladding of a siliceous optical fiber core as described in U.S. Pat. No. 4,511,209.
It is known in the art that silanol groups can be acetylated by conventional acetic anhydride or acetyl chloride reagents to yield the corresponding silyl acetates of equation (2), and a review article by E. V. Kukharskaya and A. D. Fedoseva, Russ. Chem. Rev., 32, 490 (1963) is cited for general reference. ##STR2## The silyl acetate products are described as being very moisture sensitive and more hydrophobic than the original HSR. In addition, S. Fordham, "Silicones", George Newnes Ltd.: London, p. 33 (1960) indicates that the silyl acetate groups are not very thermally stable, reverting bimolecularly to disiloxane and acetic anhydride.
It is believed that the reaction of an azlactone and a silanol group to afford a silyl 2-amidoacetate has not been previously reported.